bhastrika followed by antara kumbhaka results in a pressurized building of energy, then a powerful "surge" wherein I occasionally lose my senses for a bit (2-6 seconds)
When I come to, I'm slowly involuntarily exhaling while my whole body is buzzing. It's slightly uncomfortable.
The more breath I take in prior, the more likely the surge is to happen.
It is good to lower your breath count before antara kumbhaka at this point. Just do as many you can do for a comfortable kumbhaka. You will see over time that 1. during one session of practice you might increase the amount of breaths (e.g. first round 5 breaths before kumbhaka, second round 10 breaths before kumbhaka,...) and 2. you might be able to increase after many weeks or months of practice.
In AYP bhastrika is even done without kumbhaka. Before I found AYP I used to do bhastrika with many many breaths and kumbhaka, but since I tried the AYP version without kumbhaka, but with a longer breathing duration (several minutes) and breathing in the spine, I started to even prefer it as it is less demanding and still very effective. I found there is no point of doing intense bhastrika kumbhakas